Jeffrey P Zwerner | PubMed Health

PubMed2003

EWS/FLI function varies in different cellular backgrounds.

EWS/FLI and other EWS/ets chimeric transcription factors play a central role in the biology of the Ewing family tumors. As with many oncogenes, EWS/FLI biologic activity can be demonstrated in a limited range of cellular contexts. To investigate the causes of this restriction, we demonstrate that two immortalized fibroblast lines resistant to EWS/FLI transformation, Rat1 and Yal7, express stable levels of EWS/FLI protein. Despite their resistance to EWS/FLI, Rat1 and Yal7 can be transformed by the potent EWS/FLI downstream mediator PDGF-C. In contrast to NIH3T3, the EWS/FLI resistant lines show no upregulation of PDGF-C in response to EWS/FLI, demonstrating differential EWS/FLI function in different cellular backgrounds. This phenomenon of differential function can also be demonstrated for several other NIH3T3 targets of EWS/FLI. Despite the correlation between anchorage-independent growth and PDGF-C induction, PDGF-C does not fully reproduce all aspects of the EWS/FLI phenotype in NIH3T3 cells. These results further point to the importance of PDGF-C in mediating EWS/FLI in vitro transformation and suggest caution in assuming that a transcription factor will produce identical effects in different cellular backgrounds.

Animals↗

PubMed2002

Dominant negative PDGF-C inhibits growth of Ewing family tumor cell lines.

Nearly all cases of Ewing Family Tumors (EFT) harbor chimeric EWS/ETS transcription factors which are thought to aberrantly regulate transcriptional targets of phenotypic consequence. We have recently demonstrated that EWS/ETS proteins up-regulate platelet derived growth factor-C (PDGF-C), a novel transforming growth factor. To determine if PDGF-C signaling contributes to the malignant phenotype of EFT cell lines, we attempted to disrupt this presumed autocrine loop. AG1296, a PDGF receptor selective tyrosine kinase inhibitor, markedly inhibits anchorage-independent growth in an EFT cell line. To effect specific disruption, we have developed a dominant negative form of PDGF-C which is appropriately secreted and processed. This mutant has greatly reduced activity as a PDGF receptor agonist. When co-expressed with PDGF-C in a fibroblast transformation model, this dominant negative dramatically inhibits anchorage-independent growth. When this mutant is expressed in EFT cell lines, there is a similar reduction in anchorage-independent growth. This demonstrates that specific inhibition of PDGF-C signaling in EFT cell lines partially reverts their phenotype. These data support a significant role of PDGF-C in the biology of EFT. They also suggest that PDGF-C driven signaling may be a possible therapeutic target of more clinically relevant tyrosine kinase inhibitors.

3T3 Cells↗